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For many years the Met Office has run second-generation global
and regional wave models to provide forecasts of sea state, supporting
a range of user applications. The sea state at any point may be
thought of as the sum of many individual waves, each of a particular
direction and frequency. This can be represented as the wave energy
spectrum, where the wave energy in each frequency and each direction
is known. The Met Office wave model divides the wave energy spectrum
at each grid point into 13 frequency components and 16 direction
components. The lowest model frequency is at 0.04 Hz (25 seconds
period or 975 m wavelength), and the highest frequency resolved
by the model is 0.324 Hz (three seconds period or 15 m wavelength).
The effect of waves at higher frequencies is included in the calculation
of source terms.
The wave models account for growth of waves due to wind input,
dissipation of energy by breaking waves, and transfer of energy
between spectral components by non-linear interactions. Wave energy
is advected from one grid point to the next at the group velocity.
The wave models are run using hourly surface winds from our global
and mesoscale numerical weather prediction (NWP) models and there
are three operational wave model configurations, with different
areas and resolutions, currently in use (global, European and
for UK waters). All the models include some shallow-water physics,
namely bottom friction, refraction and shoaling. The UK waters
model additionally includes the effects of time-varying currents
on the waves. The global wave model assimilates wave height data
from the radar altimeter on the ERS-2 satellite.
Future developments to the wave model will include the assimilation
of spectral wave data from the ERS-2 Synthetic Aperture Radar
(SAR) and, later, to use ENVISAT data. A project is also ongoing
to implement the third generation WAM model within the Unified
Model framework.
Further information on the different models, and examples of
their predictions:
Real-time data from the global and regional wave models are currently
available via the Met Offices Data
and Products Distribution Service (DPDS).
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